1. Field of the Invention
This invention relates to a circuit for providing rapid detection of a malfunction in an inverter circuit of the type used in an uninterruptible power system in order to enable the inverter circuit to be turned off or shut down and the uninterruptible power system to be quickly removed from a critical bus.
2. Description of the Prior Art
Self-commutating inverter circuits of the type described in U.S. Reissue Pat. No. Re. 26,342 and assigned to the same assignee as the assignee of the present invention have been used in uninterruptible power systems. These uninterruptible power systems are capable of converting a DC voltage to an AC voltage so as to provide a reliable AC power source to a critical bus, which bus in turn provides power to a critical load, such as a computer. This critical load must have a voltage source which does not deviate in amplitude or frequency from very tight specifications in order to insure its proper operation. Thus, quite often a number or a plurality of uninterruptible power systems are used in redundant fashion to supply the critical bus and load. If, however, there is a malfunction in the inverter of any UPS system, this inverter can adversely effect the overall voltage of the critical bus, thereby endangering the continued operation of computers which receive their power from that bus. One such frequent malfunction which can occur within an inverter circuit used in a UPS system can result when one of the rectifiers in a leg of the self-commutating inverter circuit is falsely triggered ON at a time when it should not be ON. This condition can ultimately result in a shift in the output voltage or possibly the frequency of the total UPS system from its desired value.